Gastric secretion and ulcer healing in mouse stomach infected with cytotoxin expressing strain of Helicobacter pylori.

Helicobacter pylori (Hp) is a major risk factor of peptic ulcer but studies on the relation between Hp infection and gastric pathology are limited due to lack of convenient models resembling Hp infection in humans. We studied the effects of inoculation of conventional BALB/c mice with toxigenic type I Hp (cagA+ and vacA+) and non-toxigenic type II Hp (cagA- and vacA-) vs administration of vehicle on gastric secretion and healing of gastric ulcers. The gastric secretion studies were performed on mice with chronic gastric fistula before and after inoculation with toxigenic or non-toxigenic Hp strain or administration of vehicle (saline). Gastric ulcers were produced in mice inoculated with toxigenic and non-toxigenic Hp strain or vehicle and then sacrificed at day 0 and after 2, 4, 7, 14 and 28 days. Ulcer area and gastric blood flow (GBF), plasma gastrin and gastric luminal somatostatin were determined. Gastric mucosal biopsy specimens were also taken for the assessment of the presence of viable Hp using rapid urease test, the Hp-culture and the reverse transcriptase--polymerase chain reaction (RT-PCR) analysis of the signal for Hp CagA. Gastric acid output was reduced by over 50% immediately after Hp inoculation and this effect persisted during all time intervals tested, being significantly more pronounced in type I Hp-infected stomach. The area (7 mm2) of ulcers in control mice decreased gradually and then continued to decline during 14 days to disappear almost completely after 28 days. In contrast, the ulcers were present till day 28 in all mice infected with type I or type II Hp strain being significantly larger especially with type I Hp-infection. The GBF in control mice showed gradual rise with decreasing ulcer size being significantly higher at the ulcer margin than the ulcer crater and reached after 14 and 28 days the value not significantly different from that in vehicle-administered mice. In contrast, the GBF in type I Hp-infected mice but to a lesser extent, in type II Hp infected mice was significantly lower than in the vehicle controls, both at the ulcer margin and the crater of ulcers at all tested days. Hp-infection was accompanied by significant increment in plasma gastrin and the fall in gastric somatostatin contents observed at all test days, particularly in mice infected with type I Hp strain. Edema of surface epithelium appeared after 7 days and wak but significant mucosal inflammatory infiltration occurred after 14 days to further increase after 28 days, especially in type I Hp and less in type II Hp infected mice. We conclude that conventional mice with gastric ulcers can be successfully infected by both toxigenic and non-toxigenic Hp strains and this infection markedly reduces gastric acid secretion and delays healing of ulcers probably due to the fall in mucosal microcirculation in ulcer area, mucosal inflammation and impairment in gastric-somatostatin link.